In the field of a radio communication system, there is a proposal-on an HSDPA (High Speed Downlink Packet Access) in which a plurality of communication terminal apparatuses shares high-speed, large-capacity downlink channels to perform high-speed packet transmission on a downlink. The HSDPA uses a plurality of channels such as HS-PDSCH (High Speed—Physical Downlink Shared CHannel), HS-SCCH (Shared Control CHannel of HS-PDSCH) and A-DPCH (Associated—Dedicated Physical CHannel for HS-PDSCH). The A-DPCH is a DPCH (Dedicated Physical CHannel) to be used as an auxiliary channel when an HSDPA transmission is carried out and the channel configuration and handover control thereof, etc., are the same as those of the DPCH described in 3 GPP TS25.211 v5.1.0.
The HS-PDSCH is a shared channel in the downlink direction used for packet transmission. The HS-SCCH is a shared channel in the downlink direction and carries information on resource allocation (TFRI: Transport-format and Resource related Information) and information on control of H-ARQ (Hybrid-Automatic Repeat reQuest), etc.
The A-DPCH is a dedicated auxiliary channel in the uplink and downlink directions, and therefore as many A-DPCHs as users are necessary. The A-DPCH transmits pilot signals and TPC commands, etc., and in the uplink direction, it transmits an ACK signal or NACK signal, CQI (Channel Quality Indicator) signal in addition to pilot signals and TPC commands. The ACK signal is a signal indicating that a high-speed packet on an HS-PDSCH sent from a base station apparatus has been correctly demodulated by a communication terminal apparatus and the NACK signal is a signal indicating that a high-speed packet on an HS-PDSCH sent from a base station apparatus has not been correctly demodulated by a communication terminal apparatus. Furthermore, the CQI is a signal indicating a modulation scheme and coding rate of packet data that can be demodulated by each communication terminal apparatus.
In such an HSDPA communication, in order to meet demands for enhancement of communication speeds and transmission/reception of large-volume data such as moving images in recent years, packet data is sent from a base station apparatus to the user using a technology for selecting an appropriate modulation scheme and a coding rate for error correction according to the user's communication environment and an H-ARQ technology. For this reason, scheduling with regard to a decision by the user on transmission of packet data, decision on whether or not to resend packets or decision on the modulation scheme and coding rate must be made not at a control station apparatus but at a base station apparatus.
A cell which is an area in which mobile station apparatuses can communicate with one base station apparatus is further divided into a plurality of areas called “sectors.” The above described scheduling is performed sector by sector, and therefore the base station apparatus is provided with transmission/reception signal processing circuits using a plurality of A-DPCHs corresponding to their respective sectors and transmission signal processing circuits using HS-PDSCHs and HS-SCCHs. These A-DPCH, HS-PDSCH and HS-SCCH processing circuits together form one processing circuit.
Furthermore, the A-DPCH is a user dedicated channel, and therefore there are as many A-DPCHs as users. Then, when a user moves, the user may move among a plurality of sectors, and therefore processing circuits provided for each sector must secure as many A-DPCHs as all users who can communicate in the cell of each base station apparatus.
Furthermore, a user's A-DPCH which carries out an HSDPA communication is fixedly allocated for an HSDPA communication and a CQI signal, etc., is sent using the A-DPCH.
However, in the case of a conventional radio apparatus and base station apparatus, when the base station apparatus performs scheduling, the processing circuits provided for each sector must secure A-DPCHs corresponding to all users which can communicate in the cell of the base station apparatus in which those processing circuits are provided, and therefore there are constraints on the number of A-DPCHs that can be accommodated in each transmission/reception signal processing circuit depending on the scale of hardware, which results in a problem that the number of users is limited. Furthermore, even in an initial stage in which an HSDPA transmission system is introduced and there are not so many users who perform HSDPA communications, the system needs to secure the number of A-DPCHs to be used for HSDPA transmissions from the beginning in anticipation of an increase in the number of users in the future, which results in waste of equipment and in the case where the number of users increases drastically, all HSDPA systems need to be additionally provided, which results in a problem that such a system cannot flexibly respond to an increase/decrease in the number of users. Furthermore, since A-DPCHs are fixedly assigned for HSDPA communications, A-DPCH scan not be used for communications other than HSDPA communications, resulting in a problem that it is not possible to use free A-DPCHs effectively.